JavaScript implements strStr function

The strStr function is a string matching algorithm, generally used to find the first occurrence of a string in another string. Implementing this function in Javascript is very simple. This article will introduce how to use Javascript to implement the strStr function.

First of all, we can use Javascript's built-in indexOf method to implement the strStr function. This method can return the position of the first occurrence of the specified string, or -1 if the string is not found. The following is a sample code for finding substrings in a string:

function strStr(input, search) {
  return input.indexOf(search);
}

console.log(strStr("Hello world", "world")); // 6
console.log(strStr("Hello world", "foo"));   // -1

In the above code, we call the indexOf method and pass in two parameters. The first parameter is the string to be found, and the second parameter is the substring to be found. If the substring exists in the original string, indexOf returns the position of the first occurrence of the substring in the original string; otherwise, -1 is returned.

In addition to using the indexOf method, we can also use regular expressions to implement the strStr function. Regular expressions can be created using Javascript's built-in RegExp object and can be used to find parts of a string that match a pattern. The following is a sample code that uses regular expressions to implement the strStr function:

function strStr(input, search) {
  const match = new RegExp(search).exec(input);
  return match ? match.index : -1;
}

console.log(strStr("Hello world", "world")); // 6
console.log(strStr("Hello world", "foo"));   // -1

In the above code, we create a regular expression object and use the exec method to perform regular expression matching operations in the original string. . If a matching substring is found, the exec method returns an array in which the first element is the matching substring and the second element is the starting position of the matching string in the original string. We can extract the "starting position of the matching string in the original string" from here and return the result.

To sum up, there are two ways to implement the strStr function in Javascript: using the built-in indexOf method and using regular expressions. Both methods can achieve the same effect, and which method you choose depends on your specific needs and optimization requirements. Hope this article can help you understand how to implement strStr function in Javascript.

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